1. Field of the Invention
The present invention relates to a lens driving device used for a camera installed in a portable phone, a smart phone or a tablet device and the like, in particular to a lens driving device with leaf springs, wherein the leaf springs are used for elastically supporting a lens support for retaining an object lens.
2. Description of Related Art
In recent years, along with high pixelate of the camera installed in the portable phones, the smart phones or the tablet devices and the like, almost all cameras have automatic focusing function. As shown in FIG. 7, as a driving manner of a lens system with the automatic focusing function, the lens driving device using a voice coil motor in simple structure is widely adopted.
For example, as shown in FIG. 7 to FIG. 10, the lens driving device is provided with a lens support 3, a driving coil 4, a lower spring 2 and an upper spring 7, a magnet yoke 9 and a plurality of magnets 6. The lens support 3 is used for keeping a lens (not shown in the figures) at a central position and is provided with a screw thread part 3d. The driving coil 4 is installed on the lens support 3. The lower spring 2 and the upper spring 7 are installed on the lens support 3 and are used for supporting the lens support 3 from an upper position and a lower position, respectively. The magnet yoke 9 is installed around the lens support 3 and is composed of magnetic bodies such as soft iron and the like. The magnets 6 are installed within the magnet yoke 9, and an outer circumference shape of each magnet 6 is formed into a shape corresponding to the inner wall of the magnet yoke 9, and an inner circumference shape of each magnet 6 is formed into a shape corresponding to the outer circumference shape of the driving coil 4.
A shape of an outline part 2d of each lower spring 2 corresponds to the shape of a leaf spring outline retaining part 1d of a lower fixing body 1, and the outline part 2d is fixed to the lower fixing body 1. A shape of an outline part 7d of each upper spring 7 corresponds to the shape of a leaf spring outline retaining part 8d of an upper fixing body 8 installed on the magnet yoke 9, and the outline part 7d is installed on the upper fixing body 8.
Guiding parts 1b are arranged at four corners of the lower fixing body 1 and abut against guiding parts 8b configured at four corners of the upper fixing body 8, this configuration determines the whole height of the fixing body.
In the lens driving device provided with the lower springs 2 and the upper springs 7, the lower springs 2 and the upper springs 7 need to be installed stably. Therefore, the outline parts 2d of the lower springs 2, the outline parts 7d of the upper springs 7 and root parts need to be fixed at preset positions stably (with UV adhesives or thermocuring adhesive materials and the like in general) on the leaf spring outline retaining part 1d of the lower fixing body 1 and the leaf spring outline retaining part 8d of the upper fixing body 8.
The driving coil 4 is positioned closer to the inner side of the radius direction than the magnets 6, and is arranged in a magnetic field generated by the magnet yoke 9 and the magnets 6, the magnetic field is in radioactive distribution. Therefore, as shown in arrows in FIG. 8, when the driving coil 4 is electrified, the driving coil 4 generates a Lorentz force towards an object to be shot (up and down directions/ vertical direction), so that the lens support 3 can move to the preset position where the restoring forces of the upper springs 7 and the lower springs 2 are balanced.
Therefore, in the lens driving device as shown in FIG. 7 and FIG. 8, an electrified current value of the driving coil 4 is controlled so as to control the movement amount of the lens support 3, thus the position of the lens (unshown in figures) can be controlled freely.
Moreover, as shown in FIG. 8 and FIG. 10, a first clamping mechanism for limiting the movement amount in the vertical direction is provided with a clamping part (projection part) 8a for limiting the maximum movement amount of the lens on the upper fixing body 8, and a front end clamping part 3a arranged at the front end part of the lens support 3 respectively. When the clamping part 8a of the upper fixing body 8 does not move, the clamping part 8a of the upper fixing body 8 and the front end clamping part 3a of the lens support 3 are only isolated at an interval (maximum movement amount) C, and during driving, the clamping part 8a of the upper fixing body 8 abuts against the front end clamping part 3a of the lens support 3, thus the interval C is limited (the clamping part 8a cannot move at the state that the interval C is zero). Moreover, under the condition, the guiding parts 7a of the upper springs 7 are engaged with the front end clamping part 3a of the lens support 3, which determines the position of a rotate direction of the lens support 3.
Moreover, as an example that the maximum movement amount (interval C) in the vertical direction is limited, the lens support 3 is not provided with the front end clamping part 3a sometimes, so that the lower surface of the clamping part 8a of the upper fixing body 8 abuts against inner outline parts 7e of the upper springs 7 which is fixed on the upper surface of the lens support 3 (unshown in figures).
As shown in FIG. 10, generally, the lens driving device is such designed so that a second clamping mechanism used for limiting a movement amount in the planar direction abuts against the magnet yoke 9 formed by soft iron base material with the maximum strength in general, thus a bending part 9a of the magnet yoke 9 and an inner side wall part (clamping part in the side face direction) 3e of the lens support 3 are configured to separated with each other at an internal (maximum movement amount) E. That is to say, the bending part 9a of the magnet yoke 9 abuts against the inner side wall part 3e of the lens support 3, so that the interval E in the planer direction is limited (the state that the interval E is zero is formed so that the clamping part cannot move).
Moreover, in the lens driving device that the magnet yoke 9 is not provided with the bending part 9a on the inner side, in order to enable the distance between the outermost part of the lens support 3 and the inner side of the magnet yoke 9 to be the interval E, the outermost part of the lens support 3 abuts against the inner side of the magnet yoke 9 sometimes so as to limit the movement amount in the left and right direction (unshown in figures).
In the existing lens driving device using the voice coil motor, in order to prevent each component from being contacted with each other to cause magnetic hysteresis, the upper side and the lower side of the lens support 3 are connected together just by using the upper springs 7 and the lower springs 2 respectively. Therefore, after the upper fixing body 8 begins to float upwardly when being driven, during the period of moving to the interval (maximum movement amount) C, the intervals between the upper fixing body 8 and each component are retained, and the upper fixing body 8 does not contact other components.
Therefore, under the condition that the lens driving device falls down to apply an impact in the vertical direction, the front end clamping part 3a of the lens support 3 collides with the clamping part 8a of the upper fixing body 8 so as to cause damage for both parties, or cause detachment of the driving coil 4, or transfer the impact to the connected lower springs 2 or upper springs 7 leading to generate micro deformation, thus the condition that the characteristics of the lens driving device are worsened appears.
Moreover, under the impact condition in the planar direction, the impact is applied to the inner side wall part 3e of the lens support 3 and the bending part 9e of the magnet yoke 9, thus strain is generated in the inner side wall part 3e of the lens support, or a welded joint of a joint part of resin begins to be damaged, or the driving coil 4 falls off, or the impact is transferred to the connected lower springs 2 or upper springs 7 leading to generate micro deformation, thus results in the condition that the characteristics of the lens driving device are worsened.
Particularly, recently, in order to be suitable for the high pixelate of the camera, the boundary dimension of the lens driving device does not change according to market requirement, the diameter of the lens is increased as much as possible, and the lens is thinned further. Therefore, in order to unable the pushing force (driving force) to decrease as much as possible to form the lens driving device, the thickness of the part except the magnets 6 needs to be thinned greatly at the state that the shapes and sizes of the current magnets 6 are kept as much as possible.
Moreover, in order to prevent damage caused by the impact, the endurance (impact resistance) of the clamping part 8a needs to be improved, and thus the clamping part 8a needs to be thickened (the wall thickness is thickened or the width is enlarged). Therefore, under the condition that the lens is required to be in a large size along with the high pixelate of the camera, the lens driving device needs to be in a small size, and two contradictory conditions that the lens is in a large size and the lens driving device is in a small size need to be met.
As a method for alleviating the impact in the vertical direction, as shown in JP No. 2006-251728 literature, a plurality of elastic projection parts are arranged near the clamping part 8e of the upper fixing body 8, but sufficient length needs to be ensured so as to obtain sufficient elastic force since a supporting body is made of ordinary liquid crystal polymer used in the lens driving device. In the lens driving device formed above, the size must be extended in the vertical direction to obtain the elastic force, but the thickness is thinned only by keeping short and small which causes a problem on strength or formation, and thus the lens driving device is difficult to be in a small size.
Moreover, in recent years, for the lens driving devices provided with the yoke 9 at the outermost for dustproof shielding, it is difficult to form a compact damper structure on the inner side of the magnet yoke just as disclosed in JP No. 2006-251728 literature.
Moreover, as the lens driving device needs to adapt to the use of high pixel in recent smart phones, tablet devices and the like, the lens with larger lens diameter than that of a lens driving device before is used or a laminated lens with increased number of lens sheets (for example, the number of the lens sheets in the existing lens driving device is set to be four from three, and is set to be five from four). Along with the increase of the number of the sheets of the laminated lens or the amplification of the lens diameter, the dead weight of the lens is increased, and the dead weight of the lens driving device is also increased. When the dead weight of the lens driving device is increased, the impact that the lens driving device sustained is increased, the impact force increased along with the increase of the weight needs to respond, and thus the projection part as the clamping part 8a or the inner wall of the lens support 3 must be thicken so as to increase the strength, which prevents the lens driving device from being in a small size.
Therefore, in the current lens driving device, an impact strategy that will not hinder miniaturization needs to be provided.